Improvements

Improved performances
• drawing RSBrightnessSlider with a Quartz gradient
• drawing the picker gradient once and then adjusting the alpha property of the layer to select the brightness

Improved circled presentation by using layer.cornerRadius property to create the shape, and therefore reducing jigsaw effect on the edge. Also, added algorithm to compute a valid position for the selection view, either on the square or the circle shape.

Cleaned unused code.
Used UIColor built in method to convert RGB<->HSV.